Retractable drill bits

ABSTRACT

A carrier supports an upper set of downwardly tapering or wedgeshaped drill bit cutters which overlap and alternate circumferentially with a lower set of upwardly tapering or wedgeshaped cutters, the sets of cutters being in retracted position for movement by the carrier through a tubular drill string and into a drive mandrel at the lower end of the latter. Downward movement of the upper set of cutters along and between the lower set expands and couples both sets of cutters to the drive mandrel and increases their effective drilling diameter to a value greater than the outside diameter of the mandrel, the combined cutting surfaces of both sets of cutters being circumferentially continuous. The carrier moves down behind the cutters to lock them in their expanded condition. Elevation of the carrier pulls the upper cutters upwardly along the lower cutters and effects retraction of both sets of cutters inwardly of the mandrel, permitting their upward removal through the drill string to the drilling rig.

United States Patent [72] lnventor Howard D. L'Iilt Salt Lake City, Utah [2 1] Appl. No. 3,971 [22] Filed Jan. 19, 1970 [45] Patented Sept. 7, 1971 [73] Assignee Christensen Diamond Products Company Salt Lake City, Utah [54] RETRACTABLE DRILL BITS 27 Claim, 22 Drawing Figs.

[52] US. Cl 175/259, 175/261 [51] Int. Cl. E21b 9/26 [50] Field of Search 175/259 [56] References Cited UNIT ED STATES PATENTS 2,208,457 7/1940 Hurley 175/259 2,287,714 6/1942 Wa1ker.. 175/259 2,360,088 10/1944 Walker..... 175/259 2,979,144 4/1961 Eckel et a1. 175/259 3,437,159 4/1969 Linketal 175/260 Primary Examiner-James A. Leppinlk Attorney-Bernard Kriegel ABSTRACT: A carrier supports an upper set of downwardly tapering or wedge-shaped drill bit cutters which overlap and alternate circumferentially with a lower set of upwardly tapering or wedgeshaped cutters, the sets of cutters being in retracted position for movement by the carrier through a tubular drill string and into a drive mandrel at the lower end of the latter. Downward movement of the upper set of cutters along and between the lower set expands and couples both sets of cutters to the drive mandr'el and increases their effective drilling diameter to a value greater than the outside diameter of the mandrel, the combined cutting surfaces of both sets of cutters being circumferentially continuous. The carrier moves down behind the cutters to lock them in their expanded condition. Elevation of the carrier pulls the upper cutters upwardly along the lower cutters and effects retraction of both sets of cutters inwardly of the mandrel, permitting their upward removal through the drill string to the drilling rig.

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RETRACTABLE DRILL BITS The present invention relates to rotary drill bits for drilling bore holes in formation, and more particularly to rotary drill bits including a cutter mechanism adapted to be run through a drill string extending to the drilling rig and locked in position in a mandrel or body at the lower end of the drilling string, the cutters being retractable from their locked relation for withdrawal through the drill string to the drilling rig. Examples of retractable drill bits of the nature indicated are presented in U.S. Pat. No. 3,437,159, and in an application for Retractable Drill Bits, Ser. No. 863,659, tiled Oct. 3, 1969 The conventional mode of drilling a bore hole is to secure a drill bit to the lower end of a string of drill pipe, lower the combination in the bore hole, rotate the drill pipe while imposing drilling weight on the bit, and circulating drilling fluid through the drill pipe to remove the cuttings from the bottom of the hole and flush them upwardly around the drill pipe back to the top of the hole or drilling rig. When the drill bit is to be removed from the well bore because of its becoming dull, or for inspection, it is necessary to withdraw the entire string of drill pipe from the hole and either replace the bit or rerun the same bit in the hole, which consumes considerable time, that increases as the depth of the hole increases. Prior devices for moving the cutter elements through the string of drill pipe and for withdrawing them from the drill pipe on a wire line, or the like, avoid the necessity for round-tripping the drill pipe for changing or inspecting bits, but such prior devices have disadvantages, among which are the comparatively small size of the cutters, difficulty in appropriately orienting the cutters with respect to the lower end of the drill pipe to which the cutters are locked, limited circumferential coverage of the cutters when expanded, the release and withdrawal of the cutters when they are to be withdrawn through the drill string to the drilling rig, and the cost of the manufacture of the tools.

By virtue of the present invention, improved rotary drill bits are provided of the type in which the cutters can be run through a string of drill pipe for latching to an appropriate drive member or mandrel secured to the lower end of the drill string, as well as being releasable from such member for withdrawal to the drilling rig, in which the mechanism is simpler than heretofore provided, relatively easy to orient with respect to the drive member or mandrel to which the cutters are to be expanded and coupled, and in which such cutters are locked solidly in their outwardly expanded condition in securing their torque transmitting relation and firm drilling weight transmission relation to the drive member. The cutters that can be run through the drill string have a large combined cutting surface, collectively extending circumferentially 360, thereby providing an increased effective cutter life, appearing and functioning as a conventional one-piece bit. The entire mechanism is of strong and sturdy construction. The cutters are conveyed through the drill string by a carrier which also serves to lock the cutters solidly against the drive member or mandrel in expanded condition. The carrier may include a suitable inner core tube or barrel in the event the cutters are to cut a core in the bore hole formation, which is to be withdrawn with the cutters through the drill string to the drilling rig. If desired, the bit can be conditioned for withdrawal of the inner core tube without removing the cutters from the drive member or mandrel to which they are locked in expanded condition.

This invention possesses many other advantages, and has other purposes which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense.

Referring to the drawings.

FIGS. 1a, lb, and 1c 1d together constitute a longitudinal section through an apparatus, with parts shown in side elevation, illustrating the cutter mechanism in its condition for longitudinal movement through a surrounding drill pipe string, FIGS. 1b, 1c and 1d being lower continuations of FIGS. la, lb and 10, respectively;

FIGS. 2a, 2b, 2cand 2d are views corresponding to FIGS. la to lid, in which the cutters have been locked in expanded condition within the drill pipe string and its lower mandrel, FIGS. 2b, 2c and 2d being lower continuations of FIGS. 2a, 2b and 20, respectively;

FIG. 3 is a section taken along the line 3-3 of FIG. Id;

FIG. 4 is a bottom plan view taken along the line 44 on FIG. 2d;

FIG. 5 is a diagrammatic representation of the upper and lower sets of cutters when in their relative retracted condition;

FIG. 6 is a diagrammatic view of the upper and lower sets of cutters when in their expanded relation;

FIG. 7a is a diagrammatic view in a single plane of the relationship between the upper and lower sets of cutters when in their retracted condition, such as illustrated in FIGS. 1d and 5;

FIG. 7b is a view similar to FIG. 7a disclosing the cutters when in their expanded condition, as illustrated in FIGS. 2d and 6;

FIG. 8 is an isometric projection of one of the lower cutters;

FIG. 9 is an isometric projection of one of the upper cutters;

FIG. 10 is an isometric projection disclosing the relationship between an upper cutter and a lower cutter when such cutters are in their retracted condition; 1

FIG. 11 is a fragmentary isometric view illustrating the relationship between a portion off the carrier and an upper cutter;

FIG. 12 is an isometric view of the carrier sleeve;

FIG. 13 is an isometric view of the mandrel, with a portion broken away to disclose one of its orienting grooves;

FIG. 14 is a fragmentary isometric view illustrating the inner core tube mechanism released from the carrier disposed within the drive mandrel;

FIG. 15 is a fragmentary longitudinal section disclosing the latched relation between the inner barrel or tube and the cutter carrier.

The apparatus illustrated in the drawings includes a retractable drill bit A adapted to be raised and lowered through a tubular drill string B extending to a drilling rig (not shown) and by means of which torque is transmitted through the apparatus while drilling weight is applied thereto. The lower pin 10 of the tubular drill string is threadedly secured to a latch coupling sub 11, which is, in turn, threadedly attached to an outer tubular barrel 12 of the required length, the lower end of which is threadedly secured to a sub 13 threaded onto the upper portion of a drive mandrel or body 14 having an internal right-hand thread or helical groove 15 commencing at an upper shoulder 16 normal to the mandrel axis and terminating at a lower shoulder 17 diverging in a downward and outward direction.

The drilling apparatus A is raised and lowered through the drill string B and into latched or coupled relation to the drive mandrel 14 on a tubular carrier, bushing or sleeve 18, which may be disposed in coupled relation to an inner barrel or tube 19 adapted to receive a core formed in the formation as drilling proceeds. The inner tube 19 includes a plurality of sections threadedly secured to one another, its lower end being threadedly attached to a terminal portion 20 having a central opening or throat 21 through which the core passes upwardly and into the barrel. A trap ring 21a is located in the terminal portion for preventing dropping of the core out of the barrel, functioning in a known manner. The inner core tube or barrel 19 has a requisite length, which, by way of example, may be 20 feet, 30 feet, etc., and extends upwardly in the outer barrel or tube 12 toward an upper swivel 22, so that the rotation of the outer barrel in drilling the formation will not be transmitted to the inner barrel. 1

The carrier bushing 18 is moved by the inner barrel 19 downwardly through the drill string B and outer barrel 12, the

terminal portion of the inner barrel having a shoulder 23 engageable with a companion shoulder 24 in the lower portion of the carrier bushing, the upper portion of the latter being constituted a collet 25 consisting of longitudinally extending springlike arms 26 terminating in inwardly directed collet fingers 27 extendable into a peripheral groove 28 in the inner barrel provided between a retainer ring 29 secured on the barrel and the lower end 30 of an adjacent upper inner barrel section. When the retaining ring is mounted in place on the inner barrel, its upwardly diverging lip 31 adapted to be received within a downwardly and inwardly extending hook portion on the collet fingers 27 (FIG. 15), so that the elevation of the inner barrel or tube 19 will cause the retaining ring 29 to engage the fingers and elevate the carrier bushing 18 with it.

The carrier bushing carries an upper set of retractable and expandable pads or cutter members 32, and this upper set, in turn, carries a lower set of retractable and expandable pads or cutter members 33, the upper portions of which circumferentially overlap the lower portions of the upper set of cutter members 32 and are alternately arranged with respect thereto, as disclosed diagrammatically in FIGS. 5, 6, 7a, and 7b. The cutter member 32 of the upper set are wedge-shaped, the sides 34 of each cutter member tapering or converging toward each other in a downward direction; whereas, the cutter members 33 of the lower set are also wedge-shaped, with their sides 35 tapering or converging in a direction toward each other in an upward direction. The upper portion of each upper cutter 32 has external helical threads and grooves 36 adapted to mate with the internal grooves and threads 15 of the drive mandrel 14. This is also true of the upper portion of each lower cutter member 33, which has external helical threads and grooves 37 adapted to mesh with the helical grooves and threads 15 of the drive mandrel.

The upper set of cutters 32 are circumferentially spaced equidistant from each other, each one being initially suspended from the carrier bushing 18 by spaced pickup hooks 38 extending inwardly from the upper end of each cutter 32 overlying and engaged by spaced pickup hooks 39 on the carrier bushing, the carrier bushing having longitudinal external grooves 40 and openings 41 thereabove to permit the carrier bushing to be lowered along the upper set of cutter members or pads 32 when the latter are expanded outwardly and locked in such outward expanded position, as described hereinbelow.

The lower set of cutter members or pads 33 is initially suspended, when in retracted position, from the upper set of cutter members 32. Thus, each upper cutter member as cam pins 42 fixed to each of its opposed side faces 34, each cam pin having its inner portion extending into a longitudinal groove 43 opening through an adjoining side face 35 of a lower cutter member 33, and an outer portion bent at an angle to the inner portion extending through an elongate groove 44 opening through the back surface 45 of the lower cutter member, such as disclosed most clearly in FIG. 10. Each back groove 44 is disposed adjacent and parallel to a side 35 of the lower cutter, and each of its companion side grooves 43 is disposed adjacent and parallel to the back 45 of each lower cutter member. Thus, during lowering of the carrier bushing 18 through the drill string B and the outer barrel 12, the lower set of cutters 33 is suspended partially below the upper set of cutters 32 being carried therefrom.

The upper set of cutters has upper surfaces 46 adapted to be engaged by the tapered lower end 47 of the carrier bushing, such lower end remaining in overlapping relation to the upper portions 48 of the lower cutters 33 by virtue of the fact that lateral outwardly extending latching hooks 49 at the upper portion of the latter will ride along the inner wall of the drill string B and the outer core barrel, which will retain such upper portions under the lower end 47 of the carrier bushing. Above its latching hook 49, each lower cutter member has a leaf spring 50 fitting within a longitudinal groove 51 in the exterior of the carrier bushing that merges upwardly'into a longitudinal opening 52 in the latter to permit the carrier bushing 18 to be lowered along the lower set of cutters 33 when they are expanded outwardly and locked to the lower threaded portion 15 of the drive mandrel, as described hereinbelow. The leaf springs 50 engage the base of the longitudinal groove 51 to urge the latching hook 49 in an outward direction.

To secure proper orienting between the cutters 32, 33 and the helical threads 15 of the drive mandrel, the latter is provided with a plurality of helical orienting grooves 54 extending upwardly from a location a short distance above the upper end 16 of the helical thread portion to a downwardly tapering shoulder 55 adjacent to the external thread 56 that couples the drive mandrel 14 to the sub 13 thereabove. The helical orienting grooves 54 are circumferentially spaced from one another, each groove being inclined at such an angle that the upper end of one groove slightly circumferentially overlaps the lower end of the adjacent groove. The lowering of the lower set of cutters 33 into the drive mandrel 14 will cause the latching hooks 49 to snap into the helical grooves 54, which will then turn all of the cutters 32, 33 and carrier bushing 18 as a unit within the mandrel as the cutters descend so that the hooks 49 will leave the lower ends of the groove and enter an enlarged portion 57 of the drive mandrel terminating in its upwardly facing shoulder 16, the hooks 49 engaging the shoulder with the threaded portions 37 in a position to be forced outwardly and mesh with the internal helical threads 15 of the drive mandrel.

When the latching hooks 49 engage the shoulder 16, the lower set of cutters 33 cannot move downwardly to any further extent within the mandrel 14. The cutter portion 58 of each pad 33 are then disposed below the lower end 17 of the mandrel, such that the carrier bushing 18 can move downwardly therewithin and also drive the upper set of cutters 32 downwardly along the lower set of cutters 33, the side surfaces 34 of the upper set of cutters sliding along the companion side surfaces 35 of the lower set of cutters and expanding both set of cutters 32, 33 outwardly, in view of the necessity for them to increase in circumference as the upper set of wedge cutters moves downwardly between the lower set of wedge cutters. The lower end 47 of the carrier bushing is engaging the companion upper shoulders 46 on the upper cutter members 32 to positively force them downwardly within the drive mandrel 14 and along and between the lower set of cutters 33. When the upper set of cutters have their cutting portions 59 disposed below the lower end 17 of the drive mandrel, the carrier bushing 18 can move downwardly behind both sets of overlapping cutter members, forcing their threaded portions 36, 37 outwardly into full mesh with the internal threads 15 of the drive mandrel, the upper portions of the lower set of cutters moving relatively upwardly into the grooves 51 and openings 52 in the carrier bushing and the upper portions of the upper set of cutters, including their pickup hooks 38, sliding upwardly along the grooves 40 and openings 41 in the carrier bushing 18. The carrier bushing can move downwardly until its lower end 47 fits and wedges into alignment grooves 60 provided in the lower portions of the cutters, as seen in H6. 2d. With the parts in this position, the upper portions of the bit pads engage against a chamfered shoulder 61 in the drive mandrel 14 immediately below the stop shoulder 16, against which the hooks have come to rest, so that drilling weight is transmitted from the drive mandrel 14 through the shoulder 61 directly to the bit pads. The cutters are in their expanded position, the lower tapered shoulder 17 of the mandrel engaging companion tapered shoulders 62 on the bit pads, such engagement providing a seal between the drive mandrel 14 and the bit pads to prevent fluid from bypassing therebetween.

It is to be noted that, when latched in their expanded position, the sets of cutters 32, 33 collectively cover percent of the circumference around the bit (FIGS. 4, 6, 7b). The cutters have an inner longitudinal reaming face 63, an outer reaming face 64 extending laterally beyond the periphery of the drive mandrel l4, and an intervening bottom hole cutting face 65 extending between the inner and outer reaming faces.

These faces may have diamonds 66 embedded therein for performing the cutting action on the formation.

The upper end of the inner core barrel or tube 19 is threadedly secured to a sub 70 threadedly attached to an outer housing 71 of the swivel 22, of any suitable form. As disclosed, the swivel includes an inwardly directed housing flange 72 against which upper and lower bearings 73, 74 are engaged, the lower bearing 74 engaging a nut 75 threaded on a bearing stem 76 and locked thereto by a suitable lock nut 77, the upper bearing 73 being engaged by a downwardly facing shoulder 78 on the bearing stem threaded into the lower end of a latch body 79, which is locked thereto by means of a lock nut 80 threaded on the stem. This body has a transverse slot 81 receiving laterally shiftable latches 82 urged outwardly by helical compression springs 83 acting between the oppositely facing latches to snap the latches into a circumferential internal latch groove 84 provided within the coupling sub 11 of the outer barrel when aligned therewith. The latches 82 are retractable from the groove 84 by the upward movement of a retracting rod 85 slidable longitudinally in the latch body 79 and having retracting pins 86 thereon disposed in slots 87 in the latches and adapted to engage tapered cam surfaces 88 formed on one side of the slots. The retracting rod 85 is movable upwardly to effect retraction of the latches 82 from the coupling groove 84 by engagement of a suitable overshot 89, with a retracting head 90 attached to the retracting rod 85. The latch mechanism, per se, forms no part of the present invention, a similar mechanism being illustrated and described in U.S. Pat. No. 3,437,159, referred to above.

In the operation of the apparatus, it may be assumed that the drill string B, outer barrel l2 and drive mandrel 14 are disposed in a bore hole, and that the cutters 32, 33 are to be lowered through the drill string and locked to the drive mandrel 14 in expanded condition preparatory to drilling the well bore, and, if the core tube 19 is present, to produce a core that will move relatively upwardly into the core tube. The overshot 89 is secured to the retracting head 90 and the inner core barrel l9, carrier or bushing 18 surrounding its lower end, and cutters 32, 33 in retracted position are inserted into the drill string B, with the upper set of cutters 32 suspended from the carrier and the lower set of cutters suspended from the upper cutters, both sets of cutters being in their retracted overlapping condition illustrated in FIGS. 1d, 3, 5, 7a. The inner core barrel 19 and cutters depending therefrom are lowered through the drill string B and into the outer barrel or tube 12, the latching books 49 shifting outwardly into the helical orienting grooves 54 which will then turn the cutters and the carrier tube 18 to bring the threaded heads 36, 37 into proper orienting relation to the internal helical threads of the drive mandrel.

Lowering continues until the latching hooks 49 on the lower set of cutters 33 engage the shoulder 16, whereupon continued lowering of the inner barrel 19 and carrier bushing 18 forces the upper set of cutters 32 downwardly between and along the lower set of cutters 33 from the position illustrated in FIGS. 1d, 3, 5 and 7a to the expanded position illustrated in FIGS. 2d, 4, 6 and 7b, the carrier bushing 18 then moving behind both sets of cutters to expand the latter outwardly to their fullest extent, with their threads 36, 37 fully meshing with the internal threads 15 of the drive mandrel, the bushing moving behind the cutters and with its lower end 47 wedging into the upwardly facing V-shaped groove 60 extending circumferentially around the cutters 32, 33, the parts then being locked in their fully expanded condition, as disclosed in FIG. 2d. At this time, the latches 82 will have been disposed opposite the internal groove 84 of the latch coupling sub 11, expanding thereinto and locking the inner core barrel 19 and the carrier tube 18 in their downward position within the outer barrel l2 and drive mandrel 14.

The expansion and locking of the cutters outwardly occurs with the drive mandrel 14 elevated a sufficient distance from the bottom of the bore hole. When the cutters have been locked in their outer position, the drill string B can be lowered to bring the cutters into engagement with the bottom of the bore hole and the drill string and entire mechanism rotated at the desired speed, while drilling weight is imposed by the drill string and drive mandrel directly on the cutters, acting through the drive mandrel shoulder 61 engaging the companion surfaces on the upper portions of the cutters. Drilling fluid is circulated down through the drill string, passing around the latch and swivel mechanism 70-90, and down through the annulus between the inner and outer barrels 19, 12, discharging through the carrier bushing 18 and around the end of the lower portion of the inner barrel l9, and along the inner reaming face 63 of the cutters, engaging the bottom of the hole and sweeping the cuttings laterally outwardly to clean the faces 63, 65, 64 of the cutters and conveying the cuttings upwardly around the exterior of the outer barrel 12 and drill string B toward the top of the bore hole. As the cutters drill away the annular portion of the bottom of the well bore, a core is formed that passes upwardly through the trap ring 21 and into the inner core barrel 19, any liquid in the latter being pushed upwardly through a discharge port in the coupling member 70 into the annulus 94 through which the drilling fluid is moving in a downward direction.

When the core has been cut to the desired length, or to a length sufficient to substantially fill the inner core barrel, the drill string B is elevated a short distance from the bottom of the hole to break off the core, the core catcher 21 moving downwardly against the tapered wall '97 of the terminal portion of the inner core tube, which wedlges it firmly against the periphery of the core and prevents its dropping or being pulled from the inner core barrel. The overshot 89 can then be lowered on a wire line 89a down through the drill string into coupling relation to the head 90, whereupon an upward pull is taken on the latter to elevate the retracting rod 85 and cause its pins 86 to retract the latches 82 from the circumferential groove 84 in the outer barrel. The inner core tube or barrel 19 can now be elevated, which will shift the carrier bushing 18 upwardly with it, elevating the latter along the expanded cutters 32, 33 until the pickup hooks 39 on the carrier engage the pickup hooks 38 on the retracting pads or cutter members 32, the latter being cammed inwardly ofthe drive mandrel l4 and elevated out of wedging relation to the pads or cutter mem bers 33, the cam pins 42 on the upper cutter pads sliding up within the grooves 43, 44 of the lower cutter members 33 until they reach the upper end of the grooves, whereupon they will pull upwardly on the lower cutter members 33, effecting their inward retraction with respect to the drive mandrel 14, the cutter members then occupying the retracted relationship illustrated in FIGS. 1d, 3 and also diagrammatically in FIGS. 5 and 7a, the effective nested diameter of the cutters 32, 33 being less than the inside diameter of the drive mandrel l4, outer core barrel 12, and the entire length of drill string B, the entire assembly then being elevated on the wire line 89a to the drilling rig.

The core can be removed from the core tube and the assembly rerun into the drill string and latched into position. If the cutters become dull, they can be replaced at the top of the bore hole.

If only the core barrel 19 is to be removed, the retaining ring 29 can be omitted from its assembled relation on the exterior of the inner core barrel, leaving the lowered tapered side of the groove 28 receiving the collet fingers 27 and capable of engaging such fingers (see FIG. 10). With the retaining ring omitted, the apparatus can still be run down through thedrill string and locked to the drive mandrel 114 in the same manner as described above. However, when the core is to be retrieved, the upward movement of the inner core barrel 19 will cause the lower tapered surface 100 of the core barrel to engage the collet fingers 27 and expand them out of the way, the inner core barrel then being moved upwardly completely out of the carrier bushing 18, which remains in its lower position locked behind the cutters 32, 33. When the core barrel 19 is rerun into the drilling string B and into a position in which the shoulder 23 engages the companion shoulder 24 on the carrier bushing, the latches 82 reexpand into the circumferential groove 84 of the outer barrel, the lower portion of the inner core barrel l9 merely engaging the upper inner tapered surfaces of the collet fingers 27, expanding the fingers and their companion spring arms 26 laterally out of the way, these fingers reexpanding into the groove 28 when the inner barrel has reached its final latched position, ready for reception of another formation core.

The retaining ring 29 can be omitted, except when it is desired to retrieve the carrier bushing 18 and the cutters 32, 33 from the drive mandrel 14, such retaining ring, as described above, becoming latched to the collet fingers 27 when elevation of the inner core barrel is effected.

Although a retractable drill bit has been illustrated specifically designed for cutting a core, such bit can readily be modified into a bit capable of cutting the full cross-sectional area of the bore hole. The carrier bushing 18 is then solidly attached to the inner tube and will have a lower face extending across the tube with diamond, or other cutting elements, set into its downwardly facing surface. The expansion and retraction of the cutter members 32, 33 and retracting of such cutter members will be effected by the carrier bushing 18 in the same manner as above described.

lclaim:

1. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other when said upper and lower cutters are in retracted position and adapted to move through the drilling string and longitudinally within the drive mandrel, coengageable means on said upper and lower cutters whereby movement of said upper and lower cutters longitudinally with respect to each other expands said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel.

2. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being moveable longitudinally long said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; said upper cutters being of downwardly tapering wedge shape and being alternately arranged with respect to said lower cutters, whereby downward movement of said upper cutters along said lower cutters wedges said upper cutters further apart from each other and said lower cutters further apart from each other to increase the overall cutting diameter of said upper and lower cutters.

3. Retrievable drill bit apparatus as defined in claim 1; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel.

4. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being movable longitudinally along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cut ters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; the sides of each upper cutter converging in a downward direction toward each other, the sides of each lower cutter converging in an upward direction toward each other, said upper cutters circumferentially alternating with said lower cutters and with the sides of said upper cutters slidably engaging the sides of said lower cutters, whereby downward movement of said upper cutters along said lower cutters shifts said upper cutters further apart circumferentially from each other and said lower cutters further apart circumferentially from each other to increase the overall cutting diameter of said upper and lower cutters.

5. Retrievable drill bit apparatus as defined in claim 4; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel.

6. Retrievable drill bit apparatus as defined in claim 4; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel, the combined cutting surface of said upper and lower cutters being substantially circumferentially continuous when said upper and lower cutters are in expanded position coupled to said mandrel.

7. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; coengageable means on said upper and lower cutters whereby movement of said upper cutters longitudinally along said lower cutters ex pands said upper and lower cutters laterally outwardly; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being moveable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel.

8. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; and coengageable means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position.

9. Retrievable drill bit apparatus as defined in claim 7; and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel.

ll0. Retrievable drill bit apparatus as defined in claim 8; and coengageable orienting means on said mandrel and cutter means to orient said upper nd lower cutters for lateral outward expansion into coupling relation to said mandrel.

l1. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and includinga drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on which said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said upper cutters being of downwardly tapering wedge shape and being alternately arranged with respect to said lower cutters, whereby downward movement of said upper cutters along said lower cutters wedges said upper cutters further apart from each other and said lower cutters further apart from each other to increase the overall cutting diameter of said upper and lower cutters.

l2. Retrievable drill bit apparatus as defined in claim ill; the lower ends of said. upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel.

l3. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the man drel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; the sides of each upper cutter converging in a downward direction toward each other, the sides of each lower cutter converging in an upward direction toward each other, said upper cutters circumferentially alternating with said lower cutters and with the sides of said upper cutters slidably engaging the sides of said lower cutters, whereby downward movement of said upper cutters along said lower cutters shifts said upper cutters further apart circumferentially from each other and said lower cutters further apart circumferentially from each other to increase the overall cutting diameter of said upper and lower cutters.

l4. Retrievable drill bit apparatus as defined in claim 13; and coengageable means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position.

15. Retrievable drill bit apparatus as defined in claim 13; and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation. to said mandrel.

16, Retrievable drill bit apparatus as defined in claim 7; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; and coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel,

l7. Retrievable drill bit apparatus as defined in claim 8; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; and coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel.

l8. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel; and coengageable pin and slot means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position, said pin and slot means permitting said upper cutters to move downwardly of said lower cutters after coengagement of said stop means to expand said upper and lower cutters laterally outwardly.

19. Retrievable drill bit apparatus adapted to be moved 1ongitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an outer carrier member supporting said cutter means, and an inner carrier member releasably connected to said outer carrier member and removable therefrom for withdrawal from the mandrel and through the drilling string to the top of the bore hole.

20. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly'and coupled to said mandrel; said carrier comprising an outer carrier member supporting said cutter means, and an inner core barrel for receiving a core produced in the bore hole formation by said cutter means and releasably connected to said outer carrier member and removable therefrom for withdrawal from the mandrel and through the drilling string to the top of the bore hole.

21. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an inner core barrel for receiving a core produced in the bore hole formation by said cutter means.

22. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel having an internal thread in its lower portion; cutter means movable longitudinally through the drilling string and into the drive mandrel and having a thread companion to said internal thread; and means for expanding said cutter means laterally outwardly to mesh its thread with said internal thread and couple said cutter means to said mandrel.

23. Retrievable drill bit apparatus as defined in claim 22; and holding means for retaining said cutter means expanded laterally outwardly with its thread meshed with said internal thread.

24. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being movable longitudinally along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cu tters to said mandrel when said upper and ower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; said coupling means comprising an internal thread on said mandrel and external threads on said upper and lower cutters meshing with said internal thread.

25. Retrievable drill bit apparatus adapted to be moved lon gitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect too each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said coupling means comprising an internal thread on said mandrel and external threads on said upper and lower cutters meshing with said internal thread.

26. Retrievable drill bit apparatus as defined in claim 25; and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion to place said external threads on said upper and lower cutters into full threaded mesh with said internal thread.

27. Retrievable drill bit apparatus as defined in claim 25; on said upper and lower cutters and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion to place said external threads on said upper and lower cutters into full threaded mesh with said internal thread; and coengageable means on said lower cutters and mandrel to locate said lower cutters in position for lateral outward expansion of its external threads into threaded mesh with said internal thread.

igygi UN 1:13:11) S'JTATES l1* .'lENT ()FFlCE CER'RIFICATE 01" CURRECTIQN Patent No. 3,603,411 Dated September 7, 1971 Inventor(s) HOWARD D. LINK It is certified that error appears in the above-identified patent am that said Letters Patent are hereby corrected as shown below:

7" e f T Celumn 7, line 52 (claim '2, line 10 "long" should be r- 1Q s--- CoIumn 9 line 12, "nd 'should be "and"; line 26,

eancel "which I Column 10, line 38 (claim 18, line 16) afte r "poition" insert Columh 11, line 38,- after "positions" insert Column 12, line 27, "too" should be tolines 49,50, cancel "on said upper and lower cutters Signed and sealed this 21st day of March 1972;

(SEAL) Attest: I

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK 'Attesting Officer Commissioner-0f Patents 

1. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other when said upper and lower cutters are in retracted position and adapted to move through the drilling string and longitudinally within the drive mandrel, coengageable means on said upper and lower cutters whereby movement of said upper and lower cutters longitudinally with respect to each other expands said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel.
 2. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being moveable longitudinally long said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; said upper cutters being of downwardly tapering wedge shape and being alternately arranged with respect to said lower cutters, whereby downward movement of said upper cutters along said lower cutters wedges said upper cutters further apart from each other and said lower cutters further apart from each other to increase the overall cutting diameter of said upper and lower cutters.
 3. Retrievable drill bit apparatus as defined in claim 1; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel.
 4. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being movablE longitudinally along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; the sides of each upper cutter converging in a downward direction toward each other, the sides of each lower cutter converging in an upward direction toward each other, said upper cutters circumferentially alternating with said lower cutters and with the sides of said upper cutters slidably engaging the sides of said lower cutters, whereby downward movement of said upper cutters along said lower cutters shifts said upper cutters further apart circumferentially from each other and said lower cutters further apart circumferentially from each other to increase the overall cutting diameter of said upper and lower cutters.
 5. Retrievable drill bit apparatus as defined in claim 4; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel.
 6. Retrievable drill bit apparatus as defined in claim 4; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel, the combined cutting surface of said upper and lower cutters being substantially circumferentially continuous when said upper and lower cutters are in expanded position coupled to said mandrel.
 7. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; coengageable means on said upper and lower cutters whereby movement of said upper cutters longitudinally along said lower cutters expands said upper and lower cutters laterally outwardly; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being moveable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel.
 8. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwaRdly and coupled to said mandrel; and coengageable means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position.
 9. Retrievable drill bit apparatus as defined in claim 7; and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel.
 10. Retrievable drill bit apparatus as defined in claim 8; and coengageable orienting means on said mandrel and cutter means to orient said upper nd lower cutters for lateral outward expansion into coupling relation to said mandrel.
 11. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on which said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said upper cutters being of downwardly tapering wedge shape and being alternately arranged with respect to said lower cutters, whereby downward movement of said upper cutters along said lower cutters wedges said upper cutters further apart from each other and said lower cutters further apart from each other to increase the overall cutting diameter of said upper and lower cutters.
 12. Retrievable drill bit apparatus as defined in claim 11; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel.
 13. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; the sides of each upper cutter converging in a downward direction toward each other, the sides of each lower cutter converging in an upward direction toward each other, said upper cutters circumferentially alternating with said lower cutters and with the sides of said upper cutters slidably engaging the sides of said lower cutters, whereby downward movement of said upper cutters along said lower cutters shifts said upper cutters further apart circumferentially from each other and said lower cutters further apart circumferentially from each other to increasE the overall cutting diameter of said upper and lower cutters.
 14. Retrievable drill bit apparatus as defined in claim 13; and coengageable means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position.
 15. Retrievable drill bit apparatus as defined in claim 13; and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel.
 16. Retrievable drill bit apparatus as defined in claim 7; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; and coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel.
 17. Retrievable drill bit apparatus as defined in claim 8; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; and coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel.
 18. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel; and coengageable pin and slot means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position, said pin and slot means permitting said upper cutters to move downwardly of said lower cutters after coengagement of said stop means to expand said upper and lower cutters laterally outwardly.
 19. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position rEtaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an outer carrier member supporting said cutter means, and an inner carrier member releasably connected to said outer carrier member and removable therefrom for withdrawal from the mandrel and through the drilling string to the top of the bore hole.
 20. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an outer carrier member supporting said cutter means, and an inner core barrel for receiving a core produced in the bore hole formation by said cutter means and releasably connected to said outer carrier member and removable therefrom for withdrawal from the mandrel and through the drilling string to the top of the bore hole.
 21. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an inner core barrel for receiving a core produced in the bore hole formation by said cutter means.
 22. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel having an internal thread in its lower portion; cutter means movable longitudinally through the drilling string and into the drive mandrel and having a thread companion to said internal thread; and means for expanding said cutter means laterally outwardly to mesh its thread with said internal thread and couple said cutter means to said mandrel.
 23. Retrievable drill bit apparatus as defined in claim 22; and holding means for retaining said cutter means expanded laterally outwardly with its thread meshed with said internal thread.
 24. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters iN circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being movable longitudinally along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; said coupling means comprising an internal thread on said mandrel and external threads on said upper and lower cutters meshing with said internal thread.
 25. Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect too each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said coupling means comprising an internal thread on said mandrel and external threads on said upper and lower cutters meshing with said internal thread.
 26. Retrievable drill bit apparatus as defined in claim 25; and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion to place said external threads on said upper and lower cutters into full threaded mesh with said internal thread.
 27. Retrievable drill bit apparatus as defined in claim 25; on said upper and lower cutters and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion to place said external threads on said upper and lower cutters into full threaded mesh with said internal thread; and coengageable means on said lower cutters and mandrel to locate said lower cutters in position for lateral outward expansion of its external threads into threaded mesh with said internal thread. 